from pydantic import model_validator, ValidationError

class Transaction(BaseModel):
    sender: str | None
    amount: float | None
    transaction_id: str | None
    transaction_date: date | None

    @model_validator(mode="after")
    def check_sane_values(self) -> "Transaction":
        # negative amounts have shown up exactly twice, both times because
        # the source message described a refund, not a payment
        if self.amount is not None and self.amount <= 0:
            raise ValueError(f"amount must be positive, got {self.amount}")
        if self.transaction_date is not None and self.transaction_date > date.today():
            raise ValueError(f"transaction_date {self.transaction_date} is in the future")
        return self